Zur Eiweißverdauung bei Wiederkäuern im Hinblick auf die faktorielle Berechnung des Eiweißbedarfes

[The ruminal nitrogen metabolism in calves and sheep. 2. Studies in wethers]

Energetically differing rations which received ca. 45% of their crude protein from a supplement of soybean oil meal or urea were tested in a model experiment with adult wethers fitted with duodenal re-entrant cannulae or rumen cannulae resp. The N-equivalent exchange of soybean oil meal by urea in wethers resulted in a distinct increase of the NH3-N content of the rumen fluid, an increase of irreversible N losses and thus a worsening of the utilization of the available N for bacterial N-efficiency. A significant influence on duodenal NAN passage, on the apparent fermentation of the organic matter, on postruminal NAN digestibility and on the content of amino acid nitrogen as well as the amino acid composition of the duodenal NAN could not be detected. The increase of the energy level of the rations did not have a significant influence on the parameters of the ruminal N metabolism in the wethers. The studies with calves and adult wethers showed that a transposition of the parameters of ruminal N metabolism obtained to calves is not possible under the conditions given.

Determination of the dry matter disappearance and the crude protein degradability of the formaldehyde treated feeds in the rumen by in situ method

Sunflower cake (SC), horse bean (HB), and alfalfa meal (AM) were treated with rising doses of formaldehyde (F) from 0.0, 0.2 ... 2.0 g F per 100 g crude protein. We have followed the differences of crude protein solubility, its degradability and disappearance of dry matter in the rumen as well as the amount of reversible bonded F from the F dose. With AM it was found a significant influence of ADF on the degradability and on the amount of acid-labile bonded F and/or on the decrease of N solubility. From the total N content the share of soluble nitrogen decreased in SC by 31%, HB by 24%, and in AM only by 12.5%. With the increase of the F dose its protective effect on proteins against the degradability mainly in SC and HB also rose significantly. The degradability of AM protein was influenced more by the incubation time than by the effect of treatment. The degradability of the SC proteins fell from 95% with untreated to 27% treated with the maximum dose. With AM it fell slowly from 84% to 74% by the determination coefficient R2 = 0.77. It was observed a marked decrease in HB only from the dose of 1.28% F. The changes in dry matter disappearance were similar to the changes in crude protein degradability and to the changes of solubility in SC and AM. The in situ method proved very suitable for the determination of the extent of degradability of the feed proteins in the rumen.

Ruminal protein degradation and protein value of feeds

The relationship between dry matter (DM) degradation and crude protein (CP) degradation in the dairy cow's rumen was determined with a view to defining the protein value of feeds for ruminants. The nylon bag technique was applied for these studies. For all the feeds investigate (green fodder and preserves from cocks-foot, ryegrass, alfalfa/grass and meadow grass, as well as alfalfa, extracted soybean meal) a significantly positive relationship was found to exist between the levels of DM and CP degradation (r = 0.73 to 1.0). The regression coefficient b1 (CP degradation as regressor) was found to average 0.87. The positive relationship between DM degradation and CP degradation implies that microbial protein amount and unfermented feed protein at the duodenum are negatively correlated. Model calculations show that, on account of the compensation between microbial protein and feed protein at the duodenum, in feeds with a CP concentration below 200 g/kg DM, the extent of ruminal protein degradation does not exert a marked influence on duodenal protein passage. The partial calculation of the duodenal protein supply on the basis of undegraded feed protein and microbial protein, as practiced in the new models of protein evaluation, leads to systematic errors unless the relationship between DM degradation and CP degradation is considered.

Measurement of the postruminal digestibility of crude protein by the bag technique in cows

A new method has been developed which permits the crude protein digestibility of feedstuffs in the intestine of cattle to be measured with little effort in terms of samples and experimental work. It consists of welding 0.4 ... 0.8 g of the feedstuff (particle size: 125 ... 1000 micron) into polyamide fabric bags (25 X 40 mm) which are inserted via cannulae into the digestive tracts of fistulated cows from the abomasum/duodenum to the ileum or from the abomasum/duodenum to the faeces. The mean retention time of the bags in the animal was 8.5 +/- 2.7 h from the abomasum to the end of the ileum and (13.3 +/- 1.9 h from the abomasum to the faeces. Up to 15 bags per day and cow may be used. The random error of the method is 1.3% (absolute) when the measurements are performed on two animals using two bags each. Intestinal digestibilities of over 90% were measured for concentrate proteins (except linseed meal) and of 72 ... 95% for forage proteins. Post-ruminal digestion was virtually finished at the end of the small intestine.

[Nutrient digestibility and nitrogen utilization in lactating cows under restricted protein supply and subsequent refeeding]

The effects of a 17% deficiency of crude protein for four weeks on nutrient digestibility and parameters of N metabolism were investigated using four pairs of monozygotic twin cows. During a period of realimentation of three weeks with slight nutrient oversupply and a further period of three weeks with nutrient supply adjusted to the lactation trend it was examined if residual effects remain. Protein restriction enhanced the excretion of fecal dry matter by 7.7%. Total fecal nitrogen was a high in the restricted group as in the control group. Apparent digestion coefficients for dry matter, organic matter and N-free extracts were lowered by 2 to 3 percent points with deficient protein nutrition. Crude fiber and nitrogen digestibilities declined by 4.5 and 9.8 percent points, respectively. The reduction of urine nitrogen excretion amounted to 47% as consequence of a drastically diminished nitrogen content of urine. Total nitrogen retention (milk-N and body-N) was lowered by 14%. The sum of the relative nitrogen losses via faeces and urine was not different between the protein-deficient and the normal diet. The utilization of feed nitrogen for milk nitrogen excretion was 28.2% in protein deficiency and 25.9% in control feeding. After realimentation no relevant residual effects of the previous protein deficiency were found neither with respect to nutrient digestibility nor to parameters of the nitrogen balance. So far the observed permanent effect in reduced milk yield by 6% of the expected performance can not be explained with changes in digestibility or nitrogen balance.

[Effect of the content of plant crude protein in the ration on the utilization of urea by the milk cow. 1. Nitrogen digestibility and utilization of urea for bacterial protein synthesis in the rumen]

The utilisation of feed urea in the rumen was tested in 2 experiments with a total of 4 newly lactating dairy cows (13 . . . 15 and 17 . . . 19 kg resp. milk/animal and day) with rumen and duodenal re-entrant cannulae. With the energy supply remaining constant in each case, the rations in experiment A contained 8.7, 12.4 and 14.6 and those of experiment B 10.7, 13,7 and 17.1% crude plant protein in the dry matter. After the supplementation with 120 and 150 g resp. urea/animal and day there were 11.9, 15.7 and 17.8 (A) and 13.8, 16.7 and 20.2 (B) % resp. crude protein in the dry matter. The rations consisted of maize silage and a pelleted mixture of straw and concentrated feed (A) resp. maize silage, alfalfa hay and concentrated feed (B). They contained 10.3 . . . 10.6 (A) and 13.6 (B) kg dry matter with 5.6 . . . 6.0 (A) and 8.2 (B). With the increase of the crude protein level of the ration to 16.7 . . . 17.8, the absolute amount of non-NH3-N (NAN) in the duodenum increased as well. Between N-intake (g/d, x) and NAN-passage corrected by the amount of the endogenous quota (g/d, y) the relation y = 87.3 + 0.55 x (r = 0.80) could be established. NAN-passage (y) as related to N-intake decreased with the N-concentration in the dry matter of the ration (x) according to the equation y = 0.35 + 1.22x-1 (r = 0.57). 70, 62 and 61% (experiment A) and 55, 61 and 51% (experiment B) of the consumed amount of N were apparently absorbed in the intestines as NAN (without endogenous quota). The bacterial N-yield of the rumen (g, y), determined with diamino pimelic acid as microbe marker, was dependent on the consumed digestible organic matter (g, x) as follows: y = 67.3 + 0.021x (r = 0.69). There was no connection with the level of N-supply. The measuring results of the bacterial N-yield show that the utilisation rate of the urea-N decreased rapidly when there was more than 11 . . . 12% crude plant protein in the dry matter of the ration. For the tested ration type (570 . . . 600 EFUcattle/kg dry matter) the urea utilisation potential in the rumen for crude plant protein concentrations of 8.7, 10.7, 12.4, 13.4, 13.7, 14.6 and 17.1% in the dry matter was 13.0, 6.9, 4.1, 2.6, 1.3 and -9.6 g urea/kg dry matter.

[Nitrogen balance and nitrogen utilization of non-lactating and lactating cows under various feeding frequency conditions]

A cross-over trial with nine nonlactating nonpregnant cows (experiment I) and a single-reversal trial with eight lactating cows (experiment II) were conducted to study the effect of feeding frequency upon nitrogen balance. The three treatments in experiment I were twice daily forage and concentrate, twice forage and eight times concentrate, and ten times forage and concentrate per day. In experiment II the animals received their forage and concentrate in two equal feedings daily or the forage in two and the concentrate in six meals per day. The diets had a severely restricted crude fiber content of only 16% in the dry matter of the total ration. In experiment I feeding frequency had no effect on fecal or urinary nitrogen excretion, nitrogen retention and nitrogen utilization. In experiment II, the urinary nitrogen excretion was significantly decreased by 9% in response to feeding concentrate six times daily. Fecal and milk nitrogen excretion as well as nitrogen retention and utilization criteria, however, were not significantly different for the two feeding frequencies.

[Effect of crude protein on fertility and urea content of the body fluids of high-yielding cows]

A total of 36 high-yielding cows were -- post partum -- divided into two analogous groups. During the following 90 days they received rations containing 14.5 resp. 19.1% crude protein. The daily milk yield ranged between 27.8 and 28.8 kg resp. 29.4 and 31 kg FCM. The urea content of the milk reached 16.8 and 33.8, that in the blood plasma 19.7 and 38.8 mg/100 ml. The correlation between urea content in milk and blood serum was r = 0.94, between milk and urea content in urine r = 0.69. The period between gravidities of 82 days (14.4%) in contrast to 127 days (19.1%) was distinctly improved, and so was the insemination index (2.0 resp. 2.8). We consider 14.5% crude protein meet the requirement for yields of 30 kg milk, which is approximately 15% below the norm.